Composite piston



C. R. SHORT COMPOSITE PISTON Filed Feb. 19, 1926 ill stars(UlElhhhlLlElfi Hi. dHURT, F DAYTON, OHI'U, ASSIGNUR Iltl El-ENlElltMOTOR BESEARGH GUHPURAWIDN, 0F DETROIT, MICHIGAN, A WRPGBATIQW tillDELAWARE.

coosnrn I lltllUtll l'.

application filed li'ehruary l2, lllttt. tierlai Zita. nt-ltd.

invention relates to improvements in pistons ior internal-combustionengines, and particularly to the composite metal-pistons having thehead'and skirt made cit diderent metals.

tlne object is to provide an improved method of joining the head andskirt so that the joint will remain tight over the working range ofengine temperatures, although the coetticients ot expansion of themetalsinay he ditlerent.

Another oh i set of the present invention is to eliminate the use of theordinary sand core in the castingprocess o'l pistons and, consequently,eliminate the necessity ol cleaning out the interior oi the piston headto rid the same o't any sand adhering to its interior walls.

Another object of the invention is, to provide the interior surface of apiston head with a lining which iscomparatively smooth, therebysubstantially reducing carloon deposits in this portion of the piston. 1

Further objects and advantages ot the present invention will he apparentfrom the tollowi ng description, reference heing had to the accompanyingdrawings, wherein a preferred form of the present invention is clearlyshown.

in the drawings 4 Fig. l is a cross sectionalview ot the piston takenalong the line l'l at Fig. 2;

lhi g. 2 is a cross-section talren along the line 2-2 of Fig. l and 4Fig. 3 is a fragmentary sectional view of the piston slrirt flangeandits cap, this view being on a larger scale than the other views.

Referring to the drawings, numeral 20 designates the piston shirt, whichis provided with diametrically opposite piston pin hosses 21. The shirt22 is provided with an inwardly-entending circular flange 22 whichmerges into an outwardly-flared conical flange 23.. lhe angle hetweenthe conical flange 23 and the circular flange 22 will depend upon thecoetticients o't expansion oil the metals torming the head and shirt.The head,'heing usnally termed a metal at good heat conductivity, suchas aluminum, will have usually a greater coeihcient oi espansion thanthe metal oi the shirt, which may he steel, tor example. Sash heing thecase, the head 2t will tend to radially faster than the flange 23. Thiswould tend to loosen the joint hetween the flange 23 and the head 2t,were it not for the tact that the head metal received hy the :en the 2223 increases in dimensions parallel to the axis of the piston at a rategreater than the'rate oil lncrease of the dimensions oi" said grooverelative to the piston axis. lln other words, the metal of the headlocated in the groove defined hy tla'nges 22 and 23, can he caused toswell to compensate for the tendency to loosen the joint hetw-een thehead. and skirt, which tendency is due to ditlerences in radialexpansion of the head and shirt, This etlect can he produced by properlyrelating the flanges 22 and 23. The angle between these tlanges,indicated A. in idig. 3, can he determined with relation to the metalsforming the head and skirt. lit the skirt is of steel and the head isoil aluminum, the angle A is preferably 52.? de

grees.

lln pistonsoi this type, the piston head is cast on the skirt member.This casting process generally comprises placing the shirt member in asuitalole mold, then placing a core within said skirt, which. will givethe piston head the proper inside shape. The outside shape of the pistonhead is controlled, of course, by the mold, including the skirtmeniloenyWhere sand cores are used, the inner wall is generally roughand uneven, causing portions of the core to adhere thereto. Due to theformation of the interior of some pistons, it is sometimes very dithcultto removesuch adhering portions of sand and, ifthey are not removed andthe piston is so used, the lubricant might later loosen them and theywould then tend to do dama e in the engine, A rough interior in theplstoii head also quickly collects excessive carloon deposits,

which atl'ect the temperature at the vhead and thus affects oppration otthe engine.

To overcome these disadvantages, the sand core is replaced in thepresent invention, loy the use of a metal cap 25 which is adapted to heplaced in position on the flange 23. This cap is termed to the shapedesired for the interio wall ot the piston head 24. its e go, the cap 25is provided with a groove 26 which fits about the outer edge of theflange litter the cap is placed in position on the said flange, theportion of the cap oetween the groove 26 and its edge is s on over thetlange to secure the cap to the ange 23. The shirt with its cap is thenplaced in the casting mold and the piston head is then cast,

li i'orn this it may he seen that the cap 25 Adjacent tltl till

performs two functions; first, it acts as a core upon which the materialof the piston head 24 is cast, and secondly, it provides a smooth liningfor the interior of the piston head. the result of the first function,the cap maintains accurately the desired diiflefl' forms might beadopted, all coming within the scope of the claims which follow.

what is claimed is as follows:

.1. A piston having ac lindrical skirt provided adjacent one end thereofwith a circular flange merging into an outwardlfy-flarin conical flange,and having ahead 0 a meta of greater coefficient of expansion; than theSkirt and provided with a portion which fills the annular groove betweensaid flanges, said flanges being so related that the tendency of thejoint between the head and skirt to loosen due to the greater radialexpansion of the head is compensated by the tendency of said ortion toincrease in dimensions relative to t e axis of the pisto'm 2. Acomposite piston comprising a skirt and apiston head cast on said skirt;and a sheet-metal cap adapted to fit on the skirt and provide a castingform for the interior of the piston head.-

3; A composite piston comprisin a skirt including wrist pin bosses and aange at one end of said skirt, said flange extending inwardly toward theaxis of the skirt and aving a flared portion extending outwardly fromthe skirt; a cap of 'sheet metal adapted .to fit about the peripheraledge of the flared portion; and a piston head cast on the skirt 4 andcap.

4. A composite piston comprising a skirt including wristrpin bosses anda flange at one end of saidskirt, said flange extendin inwardly towardthe axis of the skirt and aving a flared portion extending outwardly.from the skirt; a cap of sheet metal having a peripheral'groove formednear its edge, said grooves being adapted to fit about the peripheraledge of the flared portion ;,and a piston head caston the skirt and cap.

.5. A piston having a skirt provided with a depression and having apiston head of a metal of greater co-efficient of expansion than theskirt and provided with a portion which fills the depression to form aninterlocking joint between the skirt and head, the abuttin walls of thehead and skirt being so arranged that the tendency of said joint toloosen due to greaterexpansion of the head in one direction iscompensated by the expansive increase in dimensions in anotherdirection.

In testimony whereof I affix my signature.

CHARLES R. SHORT.

